As most of you know, canine hip dysplasia (CHD) is the most common,
heritable orthopaedic problem seen in dogs. A previous article in
this series discussed CHD and the orthopaedic Foundation for Animals
(OFA), however as the University of Pennsylvania Hip Improvement
Program (PennHIP) method of CHD evaluation is becoming increasingly
more common, I thought it was time to have a closer look at this subject.
In 1983, Dr Gail Smith from the University of Pennsylvania School of
Veterinary Medicine began to actively research and develop a new
scientific method for the early diagnosis of CHD. Research in Dr.
Smith's lab has introduced evidence that there is a symptom free
"carrier" state for CHD and this state is undetectable
using standard diagnostic methods. The PennHIP method involves
special positioning of the dog so that the dog's passive hip laxity
(degree of "looseness" of the hip ball in the hip socket)
can be accurately measured. Research in Pennsylvania has shown that
the degree of passive hip laxity is an important factor in
determining the individual's susceptibility to develop Dejenerative
Joint Disease (DJD) later in life. Hip DJD, or osteoarthritis, is the
universally accepted confirmation of CHD.
Dogs are typically given a general anesthesia, then 3 separate
radiographs are taken:
-
Compression view where hips are pushed into the socket to show the
true depth of the socket and give an indication of the "fit"
of the head of the femur into the pelvic socket
- Distraction view using a special device which is the most
accurate view for showing the degree of passive laxity, and
- Hip Extended view to examiune for any existing joint disease.
This third view is the view the OFA currently uses to diagnose and
grade our dogs hips. PennHIP proponents state that the biomechanics
of the extended hip view are such that the radiograph may actually
give a false impression of joint tightness, and question the accuracy
of this view alone.
Radiographs are taken by a veterinarian who has been trained and
certified to take and measure these radiographic views. The PennHIP
evaluation results in a numerical Distraction Index (DI), which is a
measure of the passive hip laxity, and is expressed as a number
between 0 and 1. A DI approaching 0 would indicate no joint laxity
and very tight hips, whereas a DI near 1 indicates a high degree of
laxity and very loose hips. At the University of Pennsylvania, a
"threshold" of tightness has been identified in some
breeds, below which hip dysplasia is not found. These radiographic
evaluation(s) can be accurately performed on our dogs as early as 16
weeks of age, thus enabling us to evaluate a prospective breeding
prospect much earlier. We could, conceiveably, radiograph all
littermates and select the one with the tightest hips at 16 weeks for
our future breeding stock, and in that way select against the
tendancy for our dogs to develop CHD. Working enthusiasts could have
a puppy tested prior to purchase to determine if the dogs hips are
strong enough to stand up to a lifetime of strain, or if this dog
would do better in a home with lifestyle adjustments to minimize
disease expression.
International Canine Genetics Inc. (ICG) currently trains and
certifies veterinarians in PennHIP methods of evaluation. ICG is
currently working with many organizations to present the PennHIP
technology and hopes that the PennHIP Distraction Index will someday
be included as part of a dog's registry information, as the dog's OFA
number currently is. Presently, the hip evaluation reports are
considered confidential medical information and are released only to
the PennHIP veterinarian and the owner of the dog.
I have not had any of my dogs evaluated with this method, however I
am considering taking the ICG PennHIP course and becoming certified
myself. I will continue to get my dogs OFA certified at 24 months of
age or older, but I believe that any and all methods of testing for
heritable disease(s) are worthwhile. The more information we have on
every individual dog, the better, MORE INFORMED breeding decisions we
can make...and I will once again use this forum as an opportunity to
encourage ALL breeders to test ALL their dogs for ANY AND ALL types
of heritable disease(s), as well as to encourage prospective puppy
buyers to DEMAND pups from litters from TESTED parents ONLY!! If
education and concern for our dogs won't change some breeders minds
about testing, the threat of losing the almighty buck to breeders who
test their breeding stock sure will!!
Dr. Cathy Priddle
